The present invention relates to a dry etching method for Al.sub.x Ga.sub.1-x N(0.ltoreq.x.ltoreq.1) semiconductor.
Conventionally, the Al.sub.x Ga.sub.1-x N(0.ltoreq.x.ltoreq.1) semiconductor has been watched with keen interest as a material for light emitting diodes emitting blue light and light emitting devices emitting light of short wavelength region, and in manufacturing such devices, it is required to establish etching techniques such as mesa etching, recess etching and the like likewise the case of other compound semiconductors.
The Al.sub.x Ga.sub.1-x N semiconductor is a substance which is very stable chemically, and is insoluble in an acid such as hydrochloric acid, sulphuric acid, or hydrofluoric acid or a mixture thereof which is used normally as an etching fluid for other III-V group compound semiconductors. For this reason, for the etching techniques relating to the Al.sub.x Ga.sub.1-x N semiconductor, only the following few methods have been known.
A first method is wet etching using a solution of caustic soda, caustic potash or potassium pyrosulfate which is heated to 800.degree. C. or more. Also, a second method is electrolytic jet etching using 0.1N solution of caustic soda Then, a third method is wet etching using a mixture of phosphoric acid and sulfuric acid with a mixing ratio of 1:2 -1:5 at temperatures of 180.degree. C.-250.degree. C.
However, the above-mentioned first and second methods find a difficulty in practical use because of using a high-temperature corrosive substance. Also, the third method has a problem that the etching speed is varied greatly by a slight change in temperature. Thus, none of the above-mentioned methods has been brought into practical use.
Also, all of the above-mentioned methods employ wet etching, and therefore deficiencies peculiar to wet etching such as an occurrence of under cut cannot be eliminated.
On the other hand, for the dry etching method relating to the Al.sub.x Ga.sub.1-x N semiconductor, there is no known method at all. Prediction of selecting a gas having a desirable reaction characteristic in plasma etching is impossible because the reaction mechanism is affected by the combination and the crystalline structure of atoms of a compound semiconductor to be etched. Accordingly, prediction cannot be made on whether or not an existing reaction gas is effective for etching the Al.sub.X Ga.sub.1-x N semiconductor.